The issue of forbidden marriages in the bible, especially to relatives is not clear. For example, Leviticus forbids a man to marry his aunt, but not a woman to marry her uncle. Do you think Jacob committed incest by marrying his cousins Leah and Rachel?
This may be linked to the unfair treatment of women in the bible times and the deep-seated patriarchal society at that time. Marriage of cousins was not forbidden in biblical law. In Genesis 35:22, Jacob’s firstborn son Reuben committed incest by sleeping with his father’s concubine Bilhah. In Genesis 38, Judah, the fourth son of Jacob, mistook his own daughter-in-law Tamar for a prostitute while she was veiled, and had sex with her.
Incest in the Bible refers to sexual relations between certain close kinship relationships: I.e. parent’s daughter (including his sister), a man’s father’s wife (including his mother), and a man’s mother-in-law.
Amnon, King David’s eldest son and heir to the throne is the man who slept with his sister in the Bible. According to the book of 2nd Samuel, Amnon, raped his half-sister Tamar. After that happened, Tamar’s brother, Absalom, learned of the incident and, two years later, ordered his servants to have Amnon killed.
There is also records of people who slept with their mothers in the bible. In Genesis 35:22, Jacob’s firstborn son Reuben committed incest by sleeping with his father’s concubine Bilhah.
Female relatives have also been recorded to initiate sex on men. Two Daughters slept with their father in the bible, which is basically a case of rape by women in the bible. After Lot’s wife turned into a pillar of salt, Lot and his daughters escaped to Zoar, and end up living in a cave in the mountains. In Genesis 19:30-38 Lot’s daughters got their father drunk, and over two consecutive nights had sex with him without his knowledge. They both got pregnant.